Data Transfer In A Two-Pipe Directional Drilling System

ABSTRACT

A downhole tool for a dual member drill string for detecting information and sending a signal containing that information up a wireline. The tool comprises a beacon supported on a housing for collection of orientation information. The wireline is located within a drill stem in the housing. The beacon communicates a signal to the wireline using a slip ring or a receiver for receiving a wireless signal from the beacon. The downhole tool may have a steering feature such as a deflection shoe for changing the path of the downhole tool.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of provisional patent applicationSer. No. 61/447,762, filed on Mar. 1, 2011, the entire contents of whichare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a data transfer method and apparatusfor a two-pipe horizontal directional drilling (HDD) system.

SUMMARY OF THE INVENTION

The present invention is directed to a downhole tool for a dual memberdrill string. The drill string comprises an inner member and an outermember. The downhole tool comprises a housing coupled to the outermember, an inner drive shaft coupled to the inner member, a beaconsupported by the housing, a wireline disposed within the inner member,and a data relay connection. The beacon detects orientation informationand transfers a signal. The wireline carries the signal. A data relayconnection receives the signal from the beacon and transmits it to thewireline.

In another embodiment, the present invention is directed to a method forcommunication of data along a drill string. The drill string comprisesan inner member and an outer member. The method comprises detectinginformation at a beacon wherein the beacon is rotationally coupled tothe outer member, transmitting a signal containing the information fromthe beacon to a receiver supported on a downhole tool, wherein thereceiver is rotationally coupled to the inner member, and transmittingthe information from the receiver to a wireline for transmission ofinformation along a drill string to an operator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a boring system for use with the system of thepresent invention.

FIG. 2A is a side sectional view of a downhole tool having the datacommunication system of the invention.

FIG. 2B is a side sectional view of an alternative embodiment of adownhole tool of the present invention.

FIG. 3 is a side sectional view of a downhole tool comprising a datatransfer sub.

FIG. 4 is a perspective view of the downhole tool of FIG. 3.

FIG. 5A is a sectional side view of a downhole tool having a gyroscope.

FIG. 5B is a magnified side view of FIG. 5A.

FIG. 6A is a sectional side view of a downhole tool having a telemetryprobe attached to an inner drive shaft.

FIG. 6B is a sectional side view of a receiver for a downhole tool.

FIG. 7 is a perspective view of a dual member drill pipe in accordancewith one embodiment of the present invention.

FIG. 8 is a cutaway, sectional side view of a connection for a tooljoint having a wireline in an outer member.

FIG. 9 is a sectional side view of a dual member pipe section havingmembers which transfer electrical signals.

DETAILED DESCRIPTION OF THE DRAWINGS

Directional drilling systems which utilize a dual member drill stringfor transferring thrust and rotation from the drilling unit to the bitand drilling head for creating underground bores are disclosed in U.S.Pat. No. 5,490,569 issued to Brotherton et al., the contents of whichare incorporated by reference. Most commonly with these systems, thehousing of the dual member drill string connects to a downhole toolhaving a bend, or other feature, for biasing the drilling bit to oneside of the bore hole to create a curved bore path when the housing isadvanced forward without rotation of the housing such as the systemdisclosed in the Brotherton patent. The inner member of the dual memberdrill string is generally connected to a drill bit which cuts the soilor rock at the end of the bore hole when rotated. Such systems haveproven effective in drilling a variety of ground conditions ranging fromhomogeneous soil, to cobbles, to solid competent rock.

With reference now to FIG. 1, a boring system comprising a drillingmachine 11, a downhole tool 10 and a drill string 12. The drillingmachine 11 drives the drill string 12, which in turn operates elementsof the downhole tool 10 as described herein. The progress of such boringsystems is generally tracked using a walkover tracking system 13 whichreceives data from a transmitter located within the downhole tool 10 atthe terminal end of a drill string 12. The transmitter will sendinformation regarding the orientation of the downhole tool 10, theremaining battery life, and other information related to the drillingprocess. Generally, this information is wirelessly relayed to thesurface of the ground where an operator with a signal receiving unitpicks up the transmitted signal and converts the information into adisplay format readable by the operator. Such walkover tracking systemsare useful in many conditions, but are not desirable for conditionswhere the area above the downhole tool is not readily accessible. Suchconditions include bores made beneath bodies of water, beneath buildingsand other obstructions, and bores which are deeper than the range of thetransmitter. In these situations, it may be desirable to transmit theorientation data and drilling information along the drill pipeconnecting the downhole tool 10 and the boring unit 11 using a wireline22 (FIGS. 2A, 2B).

Usually, it is advantageous to include orientation sensors andtransmitters on the outer member of a drill string 12 or at an exteriorof a downhole tool 10 housing. However, in order to facilitate theintegrity and stability of a wireline through the drill string 12, it isadvantageous to include the wireline within the inner member of a drillstring 12. As the inner member and outer members are independentlyrotatable, it is not feasible to simply place a wireline inside theouter member, or to run a wireline from the outer member to the innermember as rotation may cause the wire to wrap around inner elements ofthe downhole tool 10 and drill string 12. Therefore, this inventionprovides a downhole tool 10 for transferring a signal sent by a beaconor transmitter on an outside of a downhole tool to a wireline on aninside of a drill string.

With reference to FIGS. 2A and 2B, embodiments of the invention whichsolve the above problem are shown. With specific reference to FIG. 2A,shown there in is a drilling tool 10 for a drill string 12. The drillstring 12 comprises an inner member 14 and outer member 16. The drillingtool comprises an inner drive shaft 18, a housing 20, a wireline 22, adata relay receiver 24, a beacon 26, a steering feature 28, and a drillbit 30. The steering feature 28 may be incorporated into the housing 20,or alternatively, be incorporated into the drill bit 30 itself asdisclosed in U.S. Pat. No. 6,827,158 to Dimitroff and Knecht. The innerdrive shaft 18 of the drilling tool 10 is connected to the inner member14 of the drill string by a torque-transmitting connection which maycomprise a slip-fit or threaded connection. Likewise, the housing 20 isconnected to the outer member 16 by a torque transmitting connectionsuch as a slip-fit, threaded, geometrical, or other connection. A beaconcover 27 is preferably formed in the housing 20 to protect the beacon 26from damage from the downhole environment.

The steering feature 28 of the downhole tool 10 biases the bit 30 to oneside of a bore path. As shown, the steering feature 28, or deflectionshoe, comprises an integrally formed bent sub, but also may comprise anexternally attached structure or a portion of the beacon cover 27.Alternatively, a housing 20 where the longitudinal axis of the innerdrive shaft 18 is offset from the longitudinal axis of the housing couldserve as the biasing mechanism. Steering feature 28 may be locatedeither in front of beacon 26 as shown in FIG. 2A, or behind the beacon.If the downhole tool 10 is advanced without rotation while the drill bit30 is rotated, a curved path is produced. As shown, the beacon 26 islocated opposite the steering feature 28. However, the beacon 26 may belocated at any known angle relative to the steering feature 28 providedthe angle is constant during operation of the bit. When using a bent subas shown, the inner drive shaft 18 will have a deflection along itslongitudinal axis as shown in FIG. 1. Alternatively, the inner driveshaft could contain a crowned spline joint, or other suitable constantvelocity angular joint, along its length to handle the transmission oftorque around the angle of the bend in the housing 20. An additional setof bearings (not shown) holding the inner drive member in axialalignment may be required.

The wireline 22 is disposed within the inner drive shaft 18 andconnected to the data relay receiver 24 and is adapted to transferinformation through the inner drive shaft 18 and inner member 14 to adrilling machine comprising an above ground receiver (not shown). Inaddition the wireline 22 may be adapted to carry electrical power fromthe uphole for the electronic components in data relay receiver 24, andin beacon 26 in those embodiments where an electrical connection existsbetween the wireline and the beacon. Alternatively, the inner driveshaft 18 and inner member 14 may themselves transfer information throughthe conduction of electric signals to and from the data relay receiver24 as discussed in the text related to FIG. 9.

The beacon 26 provides information about the downhole tool 10orientation, position, and other operational parameters of the beaconand conditions proximate the downhole tool 10. The beacon 26 is locatedin a side of the housing 20 of the downhole tool 10 as shown. The beacon26 may be end-loaded or side-loaded in the housing 20. Information issent via a data signal to a receiver, such as the data relay receiver 24or an above ground receiver 13. In a preferred embodiment, theinformation is encoded on a modulated dipole magnetic field produced bythe beacon 26. In each of the embodiments of the current invention, thebeacon 26 may be adapted such that beacon information may be transmittedto the walkover tracking system 13 and along wireline 22 substantiallysimultaneously.

In addition, the beacon 26 may be configured to provide a reading ofazimuth, or longitudinal heading of the downhole tool 10. To do this thebeacon 26 may comprise magnetic field sensors to determine the headingof the downhole tool 10 relative to the earth's magnetic field, or to anartificially induced magnetic field created by passing a current througha loop on the surface of the ground as is known in the art ofdirectional drilling. To provide an azimuth reading based on a magneticfield reading, the housing 20 and other components of the downhole tool10 are preferably composed of a durable non-magnetic material such ashigh strength austenitic stainless steel, or a nickel-based metallicalloy.

In the embodiment shown in FIG. 2A, the data relay receiver 24 isoperatively coupled to the inner drive shaft 18 and rotates with it. Thedata relay receiver 24 is configured to receive the informationtransmitted by the beacon 26. The data relay receiver 24 configures thesignal, preferably provides amplification and signal format conversion,and transmits the signal along the wireline 22 and up the drill string12. A window or slot (not shown) transparent to magnetic fields may beprovided in the housing 20 proximate the beacon 26 to facilitatecommunication between the beacon and the data relay receiver 24.

Referring now to FIG. 2B, the beacon 26 is configured for transfer ofinformation by transmission along a beacon wire 32 or wire pairdirectly. The downhole tool 10 of FIG. 2B again comprises an inner driveshaft 18, housing 20, wireline 22 and beacon 26. In this embodiment, thebeacon wire 32 from the beacon 26 passes through the housing 20 to aslip ring 34. The slip ring 34 comprises two electrically conductiveportions. A first portion 36 is secured to the inner drive shaft 18 androtates therewith for secure connection to the wireline 22. A secondportion 38 of the slip ring 34 is secured to an inner wall of thehousing 20 and connected to the beacon wire 32. The first portion 36 andsecond portion 38 rotate relative to one another but contact each otheracross a sliding electrical contact such that the slip ring 34 providesa consistent electrical connection between the wireline 22 and beaconwire 32. Alternatively, the first portion 36 connected to the innerdrive shaft 18 and the second portion 38 secured to the housing 20 maycomprise wire coils arranged in a concentric or face-to-face fashion andtransmit data between them by an inductive coupling rather than directelectrical contact.

Referring now to FIGS. 3 and 4, an alternative embodiment of the deviceis shown. In this embodiment a separate data transfer sub 50 is added tothe back of the drilling tool 10. As with FIGS. 1 and 2, various methodsof connecting the inner and outer drill string members may be used withthis embodiment. One arrangement for this type of connection is to use athreaded connection on the outer drive member and have a slip-fitconnection adapted for torque transmission on the inner drive member.Such a connection is shown in U.S. Pat. No. RE 38,418 to Deken andSewell. Alternatively, both the inner and outer members may be connectedwith threaded connections. In yet another arrangement, the inner membermay be connected using a threaded connection and the outer memberconnected using a slip-fit connection adapted to transmit torque alongthe outer member. As shown in FIG. 2B, the drill string 12 may comprisea “slip fit” configuration for connection to the data transfer sub 50and drilling tool 10. The outer member 16 comprises a series ofcastellations 52 as shown in FIG. 4 for the transmission of torque alongthe outer member. The width of the individual castellations 52 may be ofequal size, allowing the connection in any orientation. Alternatively,the mating castellation 52 may be of unique width such that the pipesmay connect in only one unique orientation.

With continued reference to FIGS. 3 and 4, a data relay receiver 54 iscontained within an appropriate cavity 56 in the data transfer sub 50.The device may receive information transmitted by the beacon 26 in thedrilling tool body 10. In FIG. 3 a slip ring 34 is shown fortransferring the information to the wireline 22. Alternatively, awireless data transmission similar to that disclosed in FIG. 2A could beused. Alternatively, the data relay receiver 54 may comprise a sensor orbeacon to determine characteristics of the downhole tool 10 without theuse of a separate beacon 26.

Referring now to FIGS. 5A and 5B, the downhole tool 10 comprises a datatransmission sub 60 attached to the rear of the drilling tool 10. Thedata transmission sub comprises a sensor package 62 comprising agyroscope 64. The gyroscope 64 may be a vibratory MEMS gyroscope, afiber optic gyroscope (FOG), or of other suitable design. An outerperiphery of the gyroscope 64 may include recessed passages 66 whichallow drilling fluid flowing through the inner member 14 and inner driveshaft 18 (FIG. 1) to flow around the sensor package 62 to the bit 30.The wireline 22 extends from the back of the sensor package 62 andproceeds uphole through the inner member 14.

When utilizing the gyroscope 64 located within the rotating inner drivemember, a special technique may be used for mapping the bore. Gyroscopicsensors are generally limited in the rate of rotation of the instrumentcan undergo and still provide an accurate measurement of angle or rateof angular movement, depending on the type of gyroscope. In addition,rotation of the drill stem while mapping may provide a completelyerroneous reading of position, since the axis of the bore hole isgenerally a linear feature with only slight curvature. One preferredtechnique for utilizing the gyroscope 64 with the sensor package 62 tomap the bore hole is given below.

When performing rotary drilling operations in rock formations, it iscommon for a driller once they have completed advancing a drill string12 to its full extent, to retract the drilling tool 10 one full joint ofpipe such that it is at the same position as at the end of theforewardmost advance of the previous pipe and then thrust the bit backdown to the bottom of the hole while pumping drilling fluid. A result ofthis action is a large surge of drilling fluid flowing back from theface of the hole. This helps to clear any cuttings which may havesettled around the drilling tool 10 during the drilling operation. Formapping the bore, the driller will advance the drilling tool 10 to theextent allowed by the drill string 12. He or she will then retract thedrilling tool as if performing a standard swab of the hole. Once thedrilling tool 10 is retracted the full length of the drill string 12,the rotation of the inner member 14 and inner drive shaft 18 will bestopped. At this time the gyroscope 64 will be powered up and allowed tosettle. The drilling tool 10 is then advanced to the bottom of the borehole without rotation of the inner drive shaft 18. As the drilling tool10 is advanced, angular changes, or rate changes transmitted by thegyroscope 64 are recorded. A carriage position transducer (not shown)located on boring unit 11 will simultaneously measure the distance ofadvance of the pipe going into the hole. The angular data, or angularrate data, from the gyroscope 64 will then be integrated with thecarriage advance distance serving as the incremental value, dx, for theintegration and the new position of the drilling tool at the end of theborehole can then be calculated in a stepwise fashion as the boreproceeds.

To facilitate steering of the drilling tool 10, the sensor package 62may also provide an indication of a roll position and, thus, theorientation of the steering feature 28 of the drilling tool. One methodfor accomplishing this task is to have the gyroscopic sensor housed in anon-magnetic material as disclosed earlier in this text. A protrusion67, or roll timing pin, composed of a ferrous, magnetic material mayextend from the interior of the data transmission sub to a position nearthe outer surface of the compartment where the gyroscopic sensor ishoused as shown in FIG. 5. In this manner, a magnetic sensing meanshoused in the gyroscopic sensor package 62 may sense the angularorientation, or clock position, of the data transmission sub 60 anddrilling tool 10 with respect to the inner drilling member 14 and thesensor package 62. If an accelerometer is also included in the sensorpackage 62, then the acceleration of gravity can provide an indicationof the orientation of the sensor package with respect to vertical.Having those two relative positions, it is then possible to calculatethe roll position of the outer drill housing. This information can alsobe sent up the wireline 22 to allow the operator to correctly orient thehousing according to whatever steering changes are required.

Alternatively, if the entire drill string 12 included outer member 16with single-orientation castellations 54 (FIG. 4) then the position ofthe castellation at the drill pipe currently in contact with boring unit11 could provide an indication of the roll position of the drilling tooldown hole. By orienting the castellations in a known manner at thedrilling unit, the roll orientation of the downhole drilling tool couldbe controlled in ground conditions where little wind up, or angulardeflection, was anticipated along the length of the drill string 12.

Referring now to FIG. 6A, a receiver housing 80 is shown. The receiverhousing 80 comprises a telemetry probe 81 connected to the inner driveshaft 18 of the downhole tool 10 just behind the bit 30. The receiverhousing 80 is rotatable with the rotation of the inner drive shaft 18.The receiver housing 80 comprises the telemetry probe 81 and thewireline 22 extending directly from the receiver, up the drill stein 18and uphole through the inner member of the drill string. The housing 80may be a separate device as shown, or integrally formed with the innerdrive shaft 18 of the downhole tool 10. An appropriate fluid seal 82 ispreferably included to prevent unintended loss of drilling fluid out ofthe receiver housing 80.

As shown in FIG. 6A, telemetry probe 81 will function much the same asthe data relay receiver 24 (FIG. 2A) previously discussed. That is, thetelemetry probe 81 will receive the information from beacon 26, convertit into appropriate format for transmission up the wireline 22, amplify,and transmit the data along the wireline. This configuration eliminatesthe need for a slip ring and the receiver housing 80 may be added orremoved from the downhole tool 10 as desired depending on whetherwireline 22 communication is needed for a particular underground bore. Abeacon 26 may be provided on the downhole tool 10 as shown, or thebeacon functions can be incorporated with the telemetry probe 81. If thetelemetry probe 81 is to act in place of beacon 26, a means of measuringthe roll angle of the housing 20, and thus, the steering member 28 ispreferably incorporated. Such a means could comprise a magnetic pickupdevice that senses a protruding ferrous feature (not shown) from housing20 to indicate a certain roll position.

With reference now to FIG. 6B, an alternative embodiment of the receiverhousing 80 of FIG. 6B is shown with an internal receiver coil. Thehousing comprises the receiver 24, operatively connected to the wireline22. The receiver comprises a coil 84, coil bobbin 86 and electronicsboard 88. The coil 84 is preferably an antenna capable of receivingsignals from the beacon (FIG. 6A). The coil 84 is supported by the coilbobbin 86 and disposed about the wireline 22. The signals aretransmitted to the electronics board 88. The electronics board 88configures the signal, preferably provides amplification and signalformat conversion, and transmits the signal along the wireline 22. Acenter wire connection 90 preferably holds the wireline 22 to theelectronics board 88 in a secure fashion. A fluid passage 87 in thecenter of the wire connection 90 allows fluid to flow forward and out ofbit 30.

Referring now to FIGS. 7 and 8, an additional embodiment of the dualmember drill string 12 is shown. In this embodiment, the dual memberdrill string 12 used comprises an outer drill pipe member 16 thatconnects with a sliding connection and comprises a feature for thetransmission of torque, such as mating castellation features. In thedisclosed embodiment, instead of passing a wire through the interiorportion of the inner drive member, a passageway is prepared along theouter pipe for routing of a signal wire or wires. One preferred methodas illustrated in FIG. 7 is to provide a slot 92 along an externalsurface of the outer member 16 deep enough to hold the wireline 22. Thedrill string 12 comprises tool joints 96. At the tool joints 96, apassageway is drilled to allow the wireline 22 to pass through to theshoulder of the drill string 12. The position of holes through male andfemale tool joint sections is consistent to allow for the wireline 22 tobe self-connecting as the drill pipe 12 sections are slid together. Byusing a drill pipe 12 configured in this manner, a beacon 26 or probeconfigured to drive a data signal along a wire or wires, as shown inFIG. 2B, may be used to eliminate the need for a slip ring (FIG. 2B) orother device to transmit the signal to a wire in the center of the innermember 14. It should be understood that the wire in the slot 92 alongthe outer member 16 will be held in place by a suitable epoxy, acrylicadhesive, or other means to keep the wire from getting damaged duringthe rotational action of the drill string 12.

With reference now to FIG. 9, a pipe joint is shown wherein the innermember 14 and outer member 16 of the drill string 12 may be used inplace of a wireline to transmit information. A contact 100 is providedat each end to allow the wireline (FIG. 2) or other conductive elementof the downhole tool 10 or drill string 12 to transmit information tothe conductive inner member 14. An inner member insulator 102 isprovided at portions of the inner member 14 which are likely to come incontact with the outer member 16. Likewise, an outer member insulatorsleeve 104 is provided to prevent portions of the outer member 16 fromcontacting the inner member 14. As illustrated in FIG. 9, the innermember 14 is a solid member and the connections for transmitting torquefrom one inner member 14 to the next in a pipe string are of a slip-fitvariety as disclosed in U.S. Pat. No. 5,682,956 by Deken and Sewell.Alternatively, the inner member may have a hollow passageway along itsinterior for the conveyance of drilling fluid along its interior.Similarly, the inner member 14 connection would not have to be a slipfit connection, but alternatively could be a threaded connection. Inaddition, the inner member 14 may comprise a threaded connection forconnection to the next inner member in a drill string 12 while the outermember 16 comprises a slip fit connection consistent with that shown inFIG. 7. In the embodiment shown in FIG. 9, it is contemplated thateither the inner 14 or outer 16 pipe member will provide the electricalsignal path and the other member will provide the return path tocomplete the circuit. To accomplish this, a slight modification to anyof the configurations shown in FIGS. 2-6B could be made where theelectrical connection from the data relay receiver 24, or telemetryprobe 81 would be made directly to the inner pipe member rather than tothe wireline.

Various modifications can be made in the design and operation of thepresent invention without departing from the spirit thereof. Thus, whilethe principal preferred construction and modes of operation of theinvention have been explained in what is now considered to represent itsbest embodiments, as herein illustrated and described, it should beunderstood that the invention may be practiced otherwise than asspecifically illustrated and described.

1. A downhole tool for a dual member drill string comprising an inner member and an outer member, the downhole tool comprising: a housing coupled to the outer member; an inner drive shaft coupled to the inner member; a beacon supported by the housing to detect orientation information and transfer a signal; a wireline disposed within the inner member to carry the signal; and a data relay connection to receive the signal from the beacon and transmit it to the wireline.
 2. The downhole tool of claim 1 wherein the data relay connection comprises a receiver coupled to the inner member.
 3. The downhole tool of claim 1 wherein the data relay connection comprises a slip ring, the slip ring comprising: a first portion coupled to the drill stem in electrical communication with the wireline; and a second portion coupled to the housing and in electrical communication with the beacon; wherein the first portion is in electrical communication with the second portion.
 4. The downhole tool of claim 1 wherein the data relay connection comprises an inductive data connection between the inner and outer members.
 5. The downhole tool of claim 1 wherein the downhole tool comprises a steering feature.
 6. The downhole tool of claim 5 wherein the steering feature is located between the data relay connection and the beacon.
 7. The downhole tool of claim 5 wherein the steering feature consists of a bend in the downhole tool.
 8. The downhole tool of claim 5 wherein the steering feature is located at an opposite side of the outer member from the beacon.
 9. The downhole tool of claim 1 wherein the data relay connection is located between the beacon and the drill string.
 10. The downhole tool of claim 1 wherein the housing comprises a castellation for transmission of torque from the outer member.
 11. The downhole tool of claim 1 wherein the beacon is located on the housing.
 12. The downhole tool of claim 11 wherein the data relay connection comprises a receiver coupled to the inner member.
 13. The downhole tool of claim 11 wherein the data relay connection comprises a slip ring, the slip ring comprising: a first portion coupled to the drill stem in electrical communication with the wireline; and a second portion coupled to the housing and in electrical communication with the beacon; wherein the first portion is in electrical communication with the second portion.
 14. The downhole tool of claim 1 further comprising a gyroscope sensor.
 15. The downhole tool of claim 1 further comprising a receiver housing coupled to the drill stem and extending beyond the housing, wherein the data relay connection is secured to the receiver housing.
 16. The downhole tool of claim 16 wherein the beacon is secured to the receiver housing.
 17. The downhole tool of claim 16 wherein the data relay connection comprises: a coil adapted to receive the signal from the beacon; and an electronics board adapted to configure the signal for transmission through the wireline.
 18. A method for communication of data along a drill string, the drill string comprising an inner member and an outer member, the method comprising: detecting information at a beacon wherein the beacon is rotationally coupled to the outer member; transmitting a signal containing the information from the beacon to a receiver supported on a downhole tool, wherein the receiver is rotationally coupled to the inner member; and transmitting the information from the receiver to a wireline for transmission of information along a drill string to an operator.
 19. The method of claim 18 wherein the signal is transmitted from the beacon to the receiver wirelessly.
 20. The method of claim 18 wherein the signal is transmitted from the beacon to the receiver through a slip ring, wherein the slip ring comprises a first portion rotationally coupled to the inner member and a second portion rotationally coupled to the outer member.
 21. The method of claim 18 wherein the signal is transmitted from the beacon to the receiver through an inductive coupling, wherein the inductive coupling comprises a first portion rotationally coupled to the inner member and a second portion rotationally coupled to the outer member.
 22. The method of claim 18 wherein the information from the beacon may be read either through an above ground receiving unit, or through a wireline within the drill string. 